U.S. patent application number 15/230043 was filed with the patent office on 2018-02-08 for blade guard having a safety feature.
The applicant listed for this patent is Robert Bosch GmbH, Robert Bosch Tool Corporation. Invention is credited to Andrew Frolov.
Application Number | 20180036906 15/230043 |
Document ID | / |
Family ID | 59564177 |
Filed Date | 2018-02-08 |
United States Patent
Application |
20180036906 |
Kind Code |
A1 |
Frolov; Andrew |
February 8, 2018 |
Blade Guard Having a Safety Feature
Abstract
A safety system is provided for a power tool having a
motor-driven cutting blade, a safety mechanism operable by a
controller to stop and/or move the cutting blade and a blade guard.
The safety system includes an electrically active surface provided
on the blade guard that is configured to change an electrical
characteristic in response to contact between the body of an
operator and the active surface. An active surface controller is
operable to provide electrical power to the electrically active
surface, to generate a signal in response to the change in the
electrical characteristic, the signal indicative of an unsafe
condition, and to transmit the signal to the controller for the
safety mechanism.
Inventors: |
Frolov; Andrew; (Glenview,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch Tool Corporation
Robert Bosch GmbH |
Broadview
Stuttgart |
IL |
US
DE |
|
|
Family ID: |
59564177 |
Appl. No.: |
15/230043 |
Filed: |
August 5, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B26D 7/24 20130101; B27G
19/02 20130101; B27G 19/08 20130101; B23Q 11/0082 20130101; B27B
5/38 20130101 |
International
Class: |
B27G 19/02 20060101
B27G019/02; B27G 19/08 20060101 B27G019/08; B27B 5/38 20060101
B27B005/38; B26D 7/24 20060101 B26D007/24; B23Q 11/00 20060101
B23Q011/00 |
Claims
1. A safety system for a power tool having a cutting blade driven
by a drive motor assembly supported on a base, a safety mechanism
operable by a controller to stop and/or move the cutting blade in
response to a signal indicative of an unsafe condition, and a blade
guard supported on the base in relation to the cutting blade, said
safety system comprising: an electrically active surface provided
on the blade guard, the electrically active surface configured to
change an electrical characteristic of said active surface in
response to contact between the body of an operator and said active
surface; and an active surface controller operable to provide
electrical power to said electrically active surface, to generate a
signal in response to said change in said electrical
characteristic, said signal indicative of an unsafe condition and
to transmit said signal to the controller for the safety
mechanism.
2. The safety system of claim 1, wherein: said electrically active
surface is a capacitive surface in which the electrical
characteristic is a capacitance of said active surface; and said
active surface controller is operable to monitor said capacitance
of said active surface and to generate said signal in response to a
change in said capacitance.
3. The safety system of claim 1, wherein said electrically active
surface is a resistive surface in which the electrical
characteristic is a voltage of a layer of said resistive surface;
and said active surface controller is operable to monitor said
voltage of said layer and to generate said signal in response to a
change in said voltage.
4. The safety system of claim 1, in which the blade guard is
supported by a mounting fork, wherein said active surface
controller is carried by said mounting fork.
5. The safety system of claim 1, further comprising a power supply
connected to said active surface controller.
6. The safety system of claim 5, wherein the power supply is a
battery supported by the mounting fork.
7. The safety system of claim 1, wherein said active surface
controller is configured to wirelessly transmit said signal to said
controller for said safety mechanism.
8. The safety system of claim 1, wherein the active surface
controller includes a switch actuatable to activate said active
surface controller.
9. The safety system of claim 1, wherein the active surface
controller includes a switch actuatable by movement of the blade
guard.
10. A power tool having a cutting blade driven by a drive motor
assembly supported on a base, a safety mechanism operable by a
controller to stop and/or move the cutting blade in response to a
signal indicative of an unsafe condition, comprising: a blade guard
supported on the base in relation to the cutting blade; and a
safety system including; an electrically active surface provided on
the blade guard, the electrically active surface configured to
change an electrical characteristic of said active surface in
response to contact between the body of an operator and said active
surface; and an active surface controller operable to provide
electrical power to said electrically active surface, to generate a
signal in response to said change in said electrical
characteristic, said signal indicative of an unsafe condition and
to transmit said signal to the controller for the safety
mechanism.
11. The safety system of claim 10, wherein: said electrically
active surface is a capacitive surface in which the electrical
characteristic is a capacitance of said active surface; and said
active surface controller is operable to monitor said capacitance
of said active surface and to generate said signal in response to a
change in said capacitance.
12. The safety system of claim 10, wherein said electrically active
surface is a resistive surface in which the electrical
characteristic is a voltage of a layer of said resistive surface;
and said active surface controller is operable to monitor said
voltage of said layer and to generate said signal in response to a
change in said voltage.
13. The safety system of claim 10, in which the blade guard is
supported by a mounting fork, wherein said active surface
controller is carried by said mounting fork.
14. The safety system of claim 10, further comprising a power
supply connected to said active surface controller.
15. The safety system of claim 14, wherein the power supply is a
battery supported by the mounting fork.
16. The safety system of claim 10, wherein said active surface
controller is configured to wirelessly transmit said signal to said
controller for said safety mechanism.
17. The safety system of claim 10, wherein the active surface
controller includes a switch actuatable to activate said active
surface controller.
18. The safety system of claim 17, wherein the active surface
controller is configured to provide power to said active surface
when the switch is not actuated.
19. The safety system of claim 10, wherein the active surface
controller includes a switch actuatable by installation or movement
of the blade guard.
Description
FIELD
[0001] This disclosure relates to power tools that incorporate a
guard to protect the operator from the working tool. In particular,
the disclosure relates to table saws that incorporate a blade guard
to help prevent operator access to the saw blade during
operation.
BACKGROUND
[0002] Power tools, such as table saws, incorporate various
features to prevent contact between the tool operator and the
moving saw blade. Thus, as shown in FIG. 1, a table saw 10 includes
a blade assembly 12 that is driven by a drive motor assembly 14
supported on a base 11. As part of the safety feature, the blade
assembly 12 of the table saw 10 includes an adjustable riving knife
16 that protects the back edge of the rotating cutting blade 13. A
blade guard assembly 20 is mounted to the riving knife 16, such as
by way of a mounting fork 30, and incorporates a blade guard 22
that is formed by a frame structure 24.
[0003] The blade guard 22 is pivotably mounted to the mounting fork
30 at a pivot mount 34 so that the blade guard can be pivoted in
the direction D between its upward position shown in FIG. 1 and its
operative position (not shown) adjacent the cutting blade 13. The
blade guard 22 further defines a guide slot 26 that receives a
guide pin 36 of the mounting fork 30 so ensure proper positioning
of the blade guard 22 as it pivots in the direction D, as shown in
more detail in FIG. 2. The frame structure 24 includes side walls
24a, 24b that are spaced apart to form a channel 24c configured so
that the side walls 24a, 24b flank the sides of the rotating blade
13 during operation. The frame structure 24 further includes a
curved leading end 24d that is adapted to contact a workpiece as it
is advanced toward the cutting blade to pivot the blade guard
upward while remaining in contact with the workpiece as the
workpiece advances. The riving knife 16 and the blade guard 22
combine to effectively shroud the cutting blade during
operation.
[0004] As a further safety feature, the blade assembly 12 and/or
the drive motor assembly 14 can incorporate an emergency safety
mechanism 48 that is operable to stop and/or retract the cutting
blade 13 within the base 11. This safety feature can be invoked
when the operator's body is within proximity of or contacts the
cutting blade 13. Examples of such safety mechanisms\ can be found
in the following U.S. Patents, the disclosures of which are
specifically incorporated herein by reference: U.S. Pat. Nos.
8,316,747; 8,291,797; and 8,186,256.
[0005] Some prior safety systems include components for detecting
the presence of the operator's body in the vicinity of the cutting
blade. For instance, U.S. Patent Nos. 8,291,797 and 8,186,256,
incorporated by reference above, disclose a detection subsystem
that includes detection electrodes capacitively coupled to the saw
blade to detect contact between the operator's body and the
rotating blade. One problem with these systems is that the operator
must still contact the moving blade in order to actuate the safety
system. Other systems utilize optical transmitters and detectors to
determine whether the operator's body has traversed an optical beam
that delineates a "safe" zone around the cutting blade. Systems
using optical beams can signal a false condition when debris
interferes with the optical beam.
[0006] There is always a need for an improved safety system for
power tools, such as table saws.
SUMMARY
[0007] A table saw includes a blade assembly driven by a motor
assembly supported on a base. The blade assembly and/or the motor
assembly are provided with a safety mechanism that neutralizes a
dangerous condition based on the proximity of the operator's body
to the blade assembly. The blade assembly includes a riving knife
and a blade guard assembly supported on the riving knife. The blade
guard assembly includes a blade guard formed by a frame structure
configured to flank the sides of the cutting blade during
operation. The frame structure includes electrically active
surfaces exposed to the operator. A control unit provides power to
the electrically active surfaces and generates a signal when the
electrical characteristic of any of the surfaces is modified. The
signal is provided to a main controller that is operable to
activate the safety mechanism upon receipt of the signal.
DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a side view of a table saw incorporating the blade
guard assembly and safety system disclosed herein.
[0009] FIG. 2 is an exploded component view of the drive motor
assembly, main controller and blade guard assembly of the table saw
shown in FIG. 1.
[0010] FIG. 3 is an enlarged perspective view of the underside of
the blade guard assembly shown in FIG. 2 according to one aspect of
the present disclosure.
[0011] FIG. 4 is a flowchart of operation of the main controller
for the safety mechanism shown in FIGS. 1-2.
DETAILED DESCRIPTION
[0012] For the purposes of promoting an understanding of the
principles of the disclosure, reference will now be made to the
embodiments illustrated in the drawings and described in the
following written specification. It is understood that no
limitation to the scope of the disclosure is thereby intended. It
is further understood that the present disclosure includes any
alterations and modifications to the illustrated embodiments and
includes further applications of the principles disclosed herein as
would normally occur to one skilled in the art to which this
disclosure pertain.
[0013] The present disclosure contemplates a safety system that is
precisely actuated when the operator's body is dangerously near the
cutting blade of the blade assembly, such as the blade assembly 12
of the table saw 10 shown in FIG. 1. The blade assembly 12 and/or
the drive motor assembly 14 include a safety mechanism 48 operable
to stop the cutting blade 13 and/or to move the cutting blade 13
away from the proximity of the operator's body, such as by
retracting the blade below the work surface 18 of the table saw 10.
The table saw 10 is provided with a main controller 50 that is
coupled to the safety mechanism 48 is operable to actuate the
safety mechanism immediately when a dangerous condition is
indicated. It can be appreciated that for the purposes of the
present disclosure the safety mechanism 48 can be any type of
mechanism that immediately stops the cutting blade or that
immediately retracts the cutting blade below the work surface, or
both.
[0014] During normal operation of the table saw, the rotating saw
blade 13 is protected by the riving knife 16 and the blade guard
22. However, the leading edge of the saw blade 13 cannot be
covered, otherwise the workpiece could not be advanced to the
blade. The leading edge of the saw blade is thus susceptible to
compromise by the operator's body, such as the operator's hands as
he/she advances the workpiece along the work surface 18 in the
direction C. The blade guard 22 is not sufficient to prevent the
operator's hands from advancing to the cutting blade, since the
blade guard must be able to pivot upward in the direction D. Thus,
in prior table saws, simply contacting the blade guard is
insufficient to prevent the operator form contacting the rotating
cutting blade.
[0015] The present disclosure contemplates providing the blade
guard with electrically active surfaces 25 in the outer face of the
frame structure 24. The side walls 24a, 24b and leading end 24d are
thus provided with electrically active surfaces 25. The surfaces 25
are configured so that contact by the operator's body causes a
change in the electrical characteristics of the surface. The
surface may be a capacitive surface in which an electrostatic field
is applied to the surface and disruption of that field by contact
with the operator results in a change in capacitance of the surface
25. The electrically active surface of this type can operate by
surface capacitance or by projected capacitance. Alternatively, the
electrically active surface may incorporate a resistive surface in
which pressure on an energized outer layer causes the outer layer
to contact an inner conductive layer, resulting in the voltage on
the inner layer. Other electrically active surfaces are
contemplated that produce a signal responsive to contact of the
surface by the operator's body. The active surface 25 may be
provided in the form of a wire mesh or an electrically active
coating.
[0016] The blade guard assembly 20 includes a power supply 40 and
controller 42 mounted within the blade guard mounting fork 30, as
shown in FIG. 3. The power supply 40 is electrically connected to
the active surfaces 25 to generate an electrostatic field
(capacitive surface) or a surface voltage (resistive surface). The
power supply may be a replaceable or rechargeable battery, or may
be a power transformer connectable to an external electrical
source.
[0017] The power supply provides power to the active surfaces
through the controller 42, and the controller 42 is configured to
monitor the relevant electrical characteristic of the electrically
active surfaces 25. Thus, in the case of a capacitive surface, the
active surface controller 42 continuously measures the capacitance
of the active surfaces, either collectively as a single surface or
individually as a series of separate surfaces. The controller 42
may be configured to compare the measured capacitance to a
predetermined value or may monitor for a change in the capacitance
irrespective of the magnitude of the measured capacitance. If the
electrically active surface is a resistive surface, the controller
42 may be configured to monitor the inner layer for a voltage.
[0018] The active surface controller 42 is configured to sense a
change in the relevant electrical characteristic of the
electrically active surface 25 and to generate a signal in response
to such change. This signal is provided to the main controller 50,
and the main controller 50 activates the safety mechanism 48 in
response to that signal. The two controllers 42, 50 are configured
to only invoke the safety mechanism when the cutting blade 13 is
operating, it being understood that there is no need for the safety
protocol if the cutting blade is inactive. However, the controller
50 may be configured to prevent activation of the cutting blade
when the active surface 25 of the blade guard 22 is being contacted
by the operator. The active surface controller 42 may thus be
always active and always operable to generate a signal indicative
of operator contact with the blade guard. The main controller 50
may then be configured to execute program instructions as shown in
the flowchart of FIG. 4 to discern whether the cutting blade is
active, in which case the safety mechanism 48 is activated upon
contact with the blade guard, whether the cutting blade is inactive
in which case the safety mechanism is not activated, and whether
the operator is in contact with the blade guard while an attempt is
made to activate the cutting blade, in which case the activation is
prevented.
[0019] The active surface controller 42 may be directly
electrically connected to the main controller 50 through
appropriate wiring, or alternatively the signal may be communicated
wirelessly between the two controllers 42, 50. Either of the
controllers 42, 50 may be further configured to generate a sensible
signal, such as an alarm sound, to be sensed by the operator. The
safety mechanism 48 will likely have fully operated to eliminate
the safety risk by the time the operator recognizes the alarm
signal. Nevertheless, actuation of a sensible alarm will provide
the operator with an explanation of the cause of the activation of
the safety mechanism.
[0020] The active surface controller 42 may be provided with a
switch 45, such as a micro-switch, that can be manually activated
by the operator when the table saw is to be operated.
Alternatively, the switch 45 may be configured to be automatically
actuated when the blade guard 22 is pivoted downward in the
direction D prior to operation of the table saw. The switch 45 may
thus be arranged to one side of the mounting fork 30 to be tripped
to its `on` position when the blade guard is pivoted downward, and
tripped to its `off` position when the blade guard is pivoted
upward to its idle position shown in FIG. 1. The switch 45 may be a
lever-type switch or may be an optical or proximity switch
configured to be tripped by movement of the blade guard relative to
the mounting fork.
[0021] As a further alternative, when the blade guard 22 is
installed on a riving knife, such as knife 16, the micro-switch 45
may be suppressed. The micro-switch may then be fully activated
when the main power to the table saw 10 is activated. The
micro-switch may also be configured to be deactivated when the saw
blade 13 is no longer rotating. In either condition, operator
contact with the blade guard 22 does not present a safety risk. In
these alternatives, the power supply 40 may provide power to the
active surface controller 42 to preliminarily activate the active
surface 25 of the blade guard. However, since the micro-switch has
been suppressed, the active surface controller 42 does not convey
any signal to the main controller 50 to initiate the safety
mechanism for the table saw. Once the micro-switch is activated and
no longer suppressed, any contact by the operator with the active
surface 25 will result in operation of the safety feature.
[0022] The present disclosure should be considered as illustrative
and not restrictive in character. It is understood that only
certain embodiments have been presented and that all changes,
modifications and further applications that come within the spirit
of the disclosure are desired to be protected.
* * * * *